Multivibrator having two levels triggering capability after initiation

ABSTRACT

Multivibrator apparatus in conjunction with a time measuring circuit utilizes two successive signals of different amplitudes to effect a control operation.

United States Patent [191 Lide et a1.

[4 1 Dec. 3, 1974 [75] Inventors: Basil M. Lide, Pittsburgh; Harry Kowalcheck, West Newton, both of Pa.

Westinghouse Electric Corporation, Pittsburgh, Pa.

[22] Filed: Apr. 30, 1970 [2]] Appl. N0.: 31,807

Related US. Application Data [62] Division of Ser. No. 453,692, May 6, 1965.

73] As'signee:

[52] US. Cl. 307/273, 307/235 [51] Int. Cl. .Q. H03k 3/10 [58] Field of Search 307/273, 235; 328/207 [56] References Cited UNITED STATES PATENTS 2,924,708 2/1960 Harrison 328/207 X 3,140,446 7/1964 Myers et al. 307/273 X 3,247,458 4/1966 Noyes, Jr. 328/207 Primary Examiner--Stanley D. Miller, Jr. Attorney, Agent, or Firm-M. J. Moran 57] ABSTRACT Multivibrator apparatus in conjunction with a time measuring circuit utilizes two successive signals of different amplitudes to effect a control operation.

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FIGBA- H68.

TRIP LEVEL MULTIVIBRATOR HAVING TWO LEVELS TRIGGERING CAPABILITY AFTER INITIATION This application is a division of copending applicationSer. No. 453,692, filed May 6, 1965, entitled Null Balance Indicating and Control Apparatus and Phase Sensitive Pulse Responsive Circuits for Use Therein, and owned by the present assignee.

This invention relates to improvements in indicating and control apparatus, and more particularly to an improved circuit employing a single transducer for providing both indication and control functions, the circuit supplying a null balance servo type of indication, the circuit including a phase sensitive pulse responsive control amplifier feature to, supply a control function which is substantially independent of the indication function.

The apparatus and circuit of the instant invention are especially suitable in instrumentation for indication and control of nuclear power plant coolant systems, although the use of the apparatus and circuits is not limited thereto. Prior art indication and control circuits and apparatus employed with nuclear power plant coolant systems, generally speaking, make use of linear open-loop circuits to provide an indication of aplant parameter. Outputsignals from linear devicesare also used to operate bistable amplifiers for control functions, such as safety shut-down. These prior art devices, circuits and systems are characterized by a number of disadvantages: All gains must be stabilized to a high degree; supply voltages must be well regulated; compensation must be provided for supply voltage frequency changes; compensation must be'provided for ambient temperaturechanges; and others.

Accuracy requirements under thewide variation of equipment ambient conditions have made refinement of the open loop systems impractical. These ambient conditions may be as follows: line voltages, 115110 percent nominal; frequency, 60 cycles percent; voltage transients, :30 percent from nominal; and ambient temperature ranges, 25 to 65C. When it is recalled that they desired overall accuracy of the output signals is, for example, one-half of 1 percent on reactor coolant temperature measurements, and Zpercent on reactor loop pressure measurements under the worstcombination'of the aboveconditions, it is apparent that these accuracy requirements under the wide variation in conditions couldbe met only by the most expensive and refined equipment.

The apparatus of the instant invention overcomes these and other disadvantages of the prior art. In summary,our apparatusin one typical application includes but is not limited to a transducer, which may be a resistance thermometer or a differential transformer, connected in a bridge circuit which contains a rheostat or potentiometerhaving an adjustable resistance value,

- will b'eseen later. In the indication portion of our apparatus, an output, of the bridge-circuit is supplied to a servo amplifier, which feeds a servo motor, which isop- 'eratively connected to a bridge arm to utilize an error chanical means, such as moving slide wires and gears, I

and is relegated to a position of secondary importance in respect to the indicating function. Such things as chart paper, pens, etc. contribute to unreliability of such devices if used for control.

2. Response time of control functions depend on the slow moving servo systems.

In summary, the circuits of our invention which provide for control set points employ the sensing element portion of the bridge with a separate manually adjustable balance arm for signal to the control point circuits. By proper choice of input impedances nearly complete isolation is provided between the indication and control functions. To obtain accurate trip point ofthe control circuits the control arm of the bridge is operated close to bridge balance by use of high'gain amplification of control bridge error and utilizing phase change of the output of the amplifier to detect a change through balance of the bridge sensing element. Thus, the higher the amplifier gain the more accurate the trip point since the bridge output approaches zero at trip as the amplifier approaches infinite gain. Dependence on gain stability of the amplifier and the bridge supply is eliminated since the trip signal occurs at bridge null with almost zero into the amplifier. I

The output signal which appears when the bridge goes through null, as detected-by the phase sensing amplifier, is supplied to a monostable multivibrator circuit and causes the monostable circuit to change from a first condition or state to a second condition or state.

' Accordingly, a primary object of our invention is to provide new and improved null-balance servo control apparatus. v

Another object is to provide a new and improved phase sensitive pulse responsive circuit for use in control applications.

An additional object isto provide a new, and improved null balance servo indication and control system especially suitable for instrumentation and control of nuclear power collant systems. i

A further object is to provide a new'and improved phase sensitive monostable multivibrator transistor circuit.

Still another object is to provide apparatus for controlling the coolant system of a nuclear power plant in which control and indication functions, while necessitating only a single transducer, are nevertheless substantially independent of each other.

Still a further object is to provide new and improved control and indicating apparatus the accuracy of which will not be substantially influenced by wide variations in ambient conditions and variations in power input.

These and other objects will become more clearly apparent after a study of the following specification, when r read in connection with the accompanying drawings, in which:

FIGS. 1A and 1B show linear open loop systems according to the prior art, the system of FIG. 1A employing a resistance thermometer bridge, and the system of FIG. 1B employing a differential transformer;

FIG. 1C shows the output of amplifier 22 plotted as a function of the input and FIG. 1D shows the output of the bistable or astable amplifier as a function input;

FIG. 2 is a schematic electrical circuit diagram of a resistance thermometer bridge and a phase sensitive monostable multivibrator transistor circuit as connected in the control portion of our invention;

FIG. 3 is a view of the circuit of FIG. 2 partially in block form as modified to employ a differential transformer as the transducing element of the bridge;

FIG. 4 is a schematic electrical circuit diagram of a phase sensitive mo nostable circuit according to another embodiment of our invention;

FIG. 5 is a block diagram of the apparatus and circuit of our invention showing both the indication and control portions of the apparatus;

FIG. 6 is a fragmentary view of a portion of the circuit of our invention according to one embodiment thereof;

FIG. 7 is a fragmentary view similar to FIG. 6 in which a differential transformer is utilized as the transducing element;

FIGS. 8A, 8B and 8C are a series of graphs illustrating the operation of the apparatus of FIG. 2 and FIG.

FIG. 9 is a fragmentary circuit portion showing a bridge arrangement suitable for use in the apparatus of FIG. 2 when employed in the complete system of FIG. 5',

FIG. 10 is an additional fragmentary bridge portion of a circuit suitable for use in the circuit of FIG. 4 when employed in the arrangement of FIG. 5; and

FIG. 11 is a fragmentary circuit diagram of a modified portion of the circuit of FIG. 2 according to an additional embodiment of the invention.

Referring now to the drawings, in which like reference numerals are used throughout to designate like parts, for a more detailed understanding of the invention, and in particular to FIG. 1A thereof which shows a prior art arrangement, a resistance thermometer bridge 21, which acts as a transducer for providing an electrical signal which varies in accordance with variations in some quantity, is'shown supplying its output to a direct current amplifier 22, which feeds a bistable or astable amplifier 23, which controls a controlled device, not shown for convenience of illustration, the direct current amplifier also providing an indication at 24 of the value of the input quantity.'lt is noted that regulated power supplies 25, 26 and 27 are required for the circuit devices including the bridge 21, the direct current amplifier 22 and the bistable or astable amplifier 23 respectively, and that means for ambient temperature compensation is provided for each of these, these ambient temperature compensating means being shown in block form at 28, 29 and 30 respectively.

Those skilled in the art will readily understand the additional complexity and expense necessitated by providing regulated power, and temperature compensation. The nature of this arrangement is shown in FIGS. 1C and 1D. In FIG. 1C, the outputof the DC. amplifier 22 is plotted as a function of input, with the desired trip point indicated by the point X. The trip point of the bistable or astable amplifier 23 is indicated in FIG. 1D, where output of the bistable or astable amplifier is shown as a function of input, the trip point being indicated at point Z.

In FIG. 18 a prior art arrangement is shown employing a differential transformer as the transducer, the differential transformer 31 supplying its output by way of frequency compensating means 36 to a bridge rectifier 32, which supplies an output to direct current amplfier 33, which supplies an output to indicator 34 and bistable amplifier 35. It is noted that the differential transformer 31 must be supplied with regulated alternating current power from source 37, and must have ambient temperature compensation by means 38. In addition, the DC. amplifier 33 must have ambient temperature compensation by means 39 and regulated power from source 40, and thebistable amplifier 35 must have ambient temperature compensation by suitable means 41 and regulated power from source 42. Curves similar to those of FIGS. 1C and 1D would represent the outputs of the'D.C. amplifier 33 and the bistable amplifier 35 respectively.

Particular reference is made now to FIG. 5, showing in block form a circuit and apparatus according to one embodiment of our invention. A resistance thermometer, which has a resistance value which varies with variations in the temperature thereof, shown in block form at 46, is connected by lead means 47 to two bridge circuits shown in block form at 48 and 49. As will be seen hereinafter, these bridges may have a common branch containing the transducer. Bridge 49 has alternating current supplied thereto by lead means 50 from power supply 51 which provides both alternating current and direct current as needed, the bridge 49 supplying its output by lead means 52 to an alternating current amplifier 53, which supplies an output by lead means 54 to a phase sensitive circuit 55 which-also has altemating current of the same frequency supplied thereto from power supply 51. When the input to the phase sensor circuit 55 is of a certain polarity and phase relationship to the alternating current, and attains a certain amplitude, the output of the phase sensor as developed on lead means 56 causes the flip-flop 57 to change from its steady state to another quasi-stable state and supply or cut off an output to a power amplifier, the output of the flip-flop 57 being supplied to the power amplifier 59 by lead means 58. Power amplifier 59 may be a silicon controlled rectifier, and associated circuitry. The output .of the power amplifier 59 is supplied by lead means 60 to the control device 61 which may be, for example, a valve controlling the temperature of the chamberor device where resistance thermometer 46 is located. Power amplifier 59 may be omitted if desired.

The aforementioned resistance thermometer 46 is also connected to an additional bridge circuit 48, which may be similar to the bridge circuit of FIG. 6. The output of the bridge 48 is supplied by lead means 78 to a servo amplifier 65 which supplies an output by lead means 66 to a servo motor shown in block form at 67. The servo motor is mechanically connected to a gear train device 68, which is operatively connected to a counting or indicating device 69, and which is also connected by mechanical coupling 70 to the arm 71 of a potentiometer in the bridge circuit, FIG. 6, to which a particular reference is made. It is seen that alternating current from source 51' is aupplied by leads 73 and 74 across a bridge consisting of resistor 75 and resistance thermometer 46 in one branch thereof, and resistor 76 and variable resistor 77 in the other branch thereof. The junction between resistor 75 and thermometer 46 is connected by way of lead 78 to one input terminal of the servo amplifier 65, whereas the junction between resistor 76 and variable resistor 77 is connected by way of lead 78' to the other input terminal of the servo amplifier 65. The arm 71, which may have the setting thereof on resistor 77 varied by mechanical linkage 70, provides for varying the total resistance of resistor 77.

It will be seen from a study of the circuit of FIG. 6

that the null balance arrangement renders the circuit independent of certain varying parameters and varying ambient and power supply conditions aformentioned. In FIG. 6, let resistor 75 have a value R and let resistor 76 have a value K,R. The resistance thermometer 46 has a value R,-and a voltage E, is developed between lead 74 and lead 78. The resistor 77 has a value K,R

and a voltage E is developed between lead 78'. and lead 74. The val'ue of E, is a function of temperature; when E, E the input to the amplifier, that is E, E is zero, and the counter 69 reads temperature. When temperature increases, R, increases, E, increases, and the difference E, E, is applied to the amplifier. The

motor runs the servo potentiometer until E, E and then stops. The counter reads the new temperature. At balance it will be noted that line voltage variations affect E, and E identically, and E, E remains zero regardless of line voltage fluctuations.

Particular reference is made now to FIG. 7, in which ing the coupling between the primary and the two sec ondaries inaccordance with changes in the position of the slug. It is seen that potentiometer. 94 is connected between leads 91 and 92, which are connected to the outer terminals of secondaries 89 and 90 respectively. In analyzing the circuit of FIG. 7, ME, be the voltage across secondary 90, E .bethe voltage across secondary 89, and E the voltage between lead 96 connected to potentiometer arm 95, and lead 92. At balance conditions, that is, no error and no input to the amplifier,

the shaft counter reads the slug position, E, E;,, where E, E, is a constant as determined beforehand by the nature of the transformer design. If the slug moves down, for example, on pressure increases, E, increases, E decreases and E, E equals a constant. Since E, now does not equal E the difference appears as an input totheservo amplifier. Output from theamplifier runs the motor toraise the arm 95 of the servo potentiometer until E E,, and the motor stops. The counter now reads the new pressure. At balance, changes in voltage or frequency, and-variations in the value of primaryresistance all affect E, andE, identically, andthe input remains E, E 0. Accordingly, the reading of the counter does not change with fluctuations in line voltage, changes in ambient temperature, or changes in the resistance of the primary.

Accordingly, it is seen that the circuit arrangement of FIG. 5, when used either with a resistance thermometer or with a differential transformer, provides for an indication which is substantially independent of variations and fluctuations in some of the factors and conditions mentioned hereinbefore, such as ambient temperature and line voltage.

Particular reference is made now to FIG. 2, in which the bridge arrangement for providing a signal which is utilized for control purposes, the phase sensor circuit,

and the monostable multivibrator circuit are shown in schematic electrical circuit diagram. An alternating current transformer, which it will be understood may be included in the power supply 51 of FIG. 5, has a primary 101 energized from any suitable alternating current source, not shown, a core 102 and secondaries 103, 104 and 105. The output of secondary 103 is applied by way of leads 106 and 107 across the two branches of a bridge arrangement, one of these branches including potentiometer 108 having movable contact or arm 109, and resistor 110. As employed herein the word branch includes two' arms of a bridge, the arms being connected in series across the source. The other branch of the bridge connected across leads 106 and 107 includes in series the resistance thermometer 46, lead 111 and resistor 112. The adjustable arm 109 of potentiometer 108 provides a means of adjusting the trip point, arm 109 being connected byway of lead 113, capacitor 114, resistor'llS and lead 116 to the base 117 of a transistor 118. Lead 116 is connected by way of capacitor 119 to lead 111, and emitter 120 is connected to lead 111.

The aforementioned secondary 105 has the terminals thereof connected to a full wave bridge rectifier generally designated 121, the' negative terminal of the bridge rectifier being connected to lead 111, the positive terminal of the bridge rectifier being connected by way of resistor 122, lead 123 and capacitor 124 to the aforementioned negative lead 1 11. It is accordingly seen that a positive potential is developed between lead 123' and the aforementioned lead 111 which forms a common negative return. Lead 123 is connected by way of resistor 125 to the aforementioned lead 116 and base 117. Lead 123 is also connected by way of resistor 126 and lead.l27 to the collector 128 of the aforementioned transistor 118.

The transistor 1 18 serves as a straight alternating current amplifier for amplifying the signal applied between the base and emitter thereof. Resistor 115 and capacitor 119 provide, if desired, phase correction, and resistor 115 may be made variable if desired. The aforementioned collector 128 is connected by way of capacitor 130 and lead 131 to the base 132 of an additional transistor 133 having emitter 134 thereof connected to lead 111 and having a collector 135. The transistor 133 provides phase sensing in a manner which will be more clearly apparent hereinafter.

The aforementioned secondary 104 has one terminal thereof connected to lead 111 and the other terminal thereof connected by way of capacitor 138, lead 139, rectifier. 140, lead 141, resistor 142 and lead 143 to the aforementioned collector 135. Resistor 144 is connected fromlead 111 to lead 139, whereas resistor 145 is connected from lead 111 to lead 141.

The aforementioned lead 123 is connected by way of resistor 146, lead 147 and resistor 148 to the aforementioned lead 131 and base 132. Lead 147 is connected by way of rectifier 150 and lead 151 to the arm 152 of a rheostat 153 having one end thereof connected by way of lead 154 and resistor 155 to the aforementioned lead 123. Lead 151 has capacitor 136 connected therefrom to ground 205.

The aforementioned collector 135 and lead 143 are connected by way of resistor 160, rectifier 161 and lead 162 to the base 163 of a transistor 164 having an emitter 165 connected to lead 111. The aforementioned lead 162 and base 163 are connected by way of resistor 166, lead 167, capacitor 168, lead 169 and resistor 170 to the aforementioned lead 123, which as aforementioned, is at a positive potential with respect to lead 111. The aforementioned transistor 164 has a collector 172 connected to the aforementioned lead 154. Collector 172 and lead 154 are connected by way of resistor 174 to the base 175 of a transistor 176. The emitter 177 of transistor 176 is connected to the aforementioned lead 111, while the collector 178 of the transistor 176 is connected to the aforementioned lead 169, thence to output terminal 179, and thence to utilization and control device 188, terminal 181, and lead 111, Device 188 may control the temperature at 46. A rectifier 180 is connected between the aforementioned lead 167 and lead 111 for purposes to become hereinafter more clearly apparent.

In the circuit of FIG. 2, bridge output is developed between leads 113 and 111, and after some slight phase shift, if desired, at 115-119, is amplified by transistor 118. It is noted that transistor 118 is an NPN transistor; the positive potential from lead 123 by way of resistor 125 applied to the base 117 forward biases the emitter 120.

Transistor 133 is a phase sensor. A pulsating direct current potential, obtained by half wave rectification of an alternating current potential of the same frequency as that applied to the bridge, is applied to the collector 135. Base 132 is normally biased slightly beyond saturation from lead 123 by way of resistor 146, lead 147, and resistor 148. Accordingly, it will be seen that positive alternations of the signal occurring on base 132 simultaneously with the application of a DC. pulse to the collector cause no substantial output since the transistor is already at saturation. On the other hand, negative alternations of the signal on the base occurring simultaneously with the DC. pulses of half wave rectified A.C. on the collector produce an output, since during the negative alternations, the base is not at saturation bias.

Transistors 164 and 176 comprise a multivibrator or flip-flop circuit. Rectifier 161 limits the current path in this portion of the circuit, while rectifier 180 provides a discharge path for capacitor 168 so that the circuit may readily change in either sense between states.

The circuit of potentiometer 153 and rectifier 150 is an adjustable means for changing the bias point of sensor transistor 133. When transistor 164 becomes conductive lead 154 falls in potential below that of lead 147; in accordance with the polarity of recitifer 150 current flows, increasing the voltage drop across resistor 146 and changing the bias on base 132 of transistor 133, that is, making the base less positive; the bias on transistor 133 decreases toward saturation, so that thereafter the flip-flop will substantially remain on" or in its quasi-stable state when the input signal decreases below the original trip on value. Hence an adjustable means, potentiometer 153, is provided to control the trip off point.

In more fully understanding the operation of the circuit of FIG. 2, it should be recalled that the purpose of this circuit is to cause the multivibrator comrpising transistors 164 and 176 to switch from its stable state to its quasi-stable state when a signal of at least a predetermined amplitude and of the proper phase appears between arm 109 and lead 111. It will be understood that in one mode of operation where arm 109 is initially adjusted for zero signal output, depending upon whether the bridge is off balance in one sense or direction, or in the other direction, that is, whether the resistance value of 46 increases or decreases from its initial balance value, the phase of the signal between lead 111 and 113 reverses or changes 180 degrees.

Particular reference is made now to FIG. 8A, showing signal conditions when the bridge is below balance in one sense or direction, where the curve A of the group of waveforms represents the bridge output, curve B indicates the amplifier output of amplifier 118, curve C the DC. pulse output of rectifier 140, and curve D the output of phase sensor transistor 133, or E,., the collector voltage, all plotted on the same time scale' FIG. 8B shows similar signals A, B, C and D at bridge balance, and FIG. 8C shows the signal A", B, C", and D" when the bridge is above balance. When the bridge is above balance and a negative alternation of the output of amplifier 118 is applied to base 132 coincident with a positive pulse applied to collector 135, an output D is obtained from transistor 133. If the input A" is of sufficient amplitude, the outupt D" exceeds the trip level, as shown, causing the multivibrator to change between states.

By suitable choice of component values, polarities and lead connections, it is arranged so that phase sensitive transistor 133 has an output when the bridge is unbalanced in the desired direction, that is, the direction at which it is desired to utilize some result or indication thereof and in at least a predetermined amount. The amount of required unbalance determines the trip point, which can also be adjusted within limits by arm 109. The control function occurs when the trip point is reached. The output of transistor 133 is applied by way of resistor and rectifier 161 to the base of transistor 164, the first transistor of a flip-flop" circuit including also transistor 176. The operation of the "flip-flop" or monostable multivibrator circuit is to some extent unconventional. The base of the input transistor is coupled by way of resistor 166 and capacitor 168 to the collector 178 of the second transistor 176, whereas the collector 172 of the first transistor 164 is coupled by way of resistor 174 to the base of the second transistor 176, in accordance with conventional flip-flop circuitry. Accordingly, the voltage at terminal 179 connected to collector 178 varies between two values depending upon which of the transistors 164 or 176 is conducting. While transistor 176 is conductive a very small voltage drop takes place across the transistor and accordingly terminal 179 is at substantially zero voltage with respect to terminal 181. When transistor 176 becomes non-conductive, terminal 179 rises to a relatively high voltage with respect to lead 111 and terminal 181.

Before trip on transistor 164 is not conducting.- When it becomes conductive, it remains conductive until capacitor 168 is charged throughresistor 166, whereupon the circuit restores itself automatically to its original state. If the signal is still present at lead 131, the next pulse or next negative alternation on base 132 causes the flip flop to again render transistor 164 conductive.

The apparatus or equipment to be controlled, or the element to be controlled, shown in block form as a utilization and control device 188 is operatively connected'to the terminals 179 and 181. If desired, an emitter-follower transistor circuit may be connected between these terminals having, for example, a relay winding in circuit therewith. If desired, the output of the circuit as developed across terminals 179 and 181 may be applied to a controlled rectifier, for example, a silicon rectifier having a relay inthe main current path thereof and a manually operated reset switch for breaking the circuit through the controlled rectifier to restore it to a non-conductive condition. Any other suitable terminating device may be employed for utilizing the signal output of the circuit of FIG. 2 to control a controlled element.

Particular reference is made now to FIG. 3 which shows the circuit of FIG. 2 including the flip-flop amplifier connected to a differential transformer to obtain a control signal therefrom. In FIG. 3 the primary 191 has a slug 192 with mechanical linkage 193, and two secondaries 194 and 195 connected by lead 196. Lead 196 is connected to one input terminal of the apparatus shown in block form at 190, which may include an amplifier similar to 118, a phase sensor similar to 133, a flip-flop similar to 164-176, and a controlled device, and lead 196 may correspond to lead 111 of FIG. 2. Across the two secondaries is connected, in series, the potentiometer 197 and resistor 198. The arm 199 of the potentiometer is connected by lead 200 to the other input terminal of the apparatus 190, lead 200 corresponding to lead 113 of FIG. 2.

In the operation of the circuit of FIG. 3, as the slug some variable, which results in movement being transmitted to the slug through the coupling 193, the signals from the two secondaries 194 and 195 become unbalanced and an unbalance signal is developed'between leads 1% and 200 which is supplied to the input transistor corresponding to 118.

Particular reference is made now to' FIG. 4 showing a modification of, the circuit of FIG-2, in which an additional transistor is provided to take control after the unbalance reaches at least a predetermined degree and the multivibrator circuit has changed between states as a result of that unbalance. In FIG. 4, an alternating current voltage is applied between the leads 201 and 202; across these two leads is connected one branch of a 192 moves in response to variations in the value of bridge circuit including resistor 203, lead 204 connected to ground205, and resistance thermometer 206 which, it is understood, has a resistance value which varies in accordance with variations in a quantity, which variations are to be utilized for control purposes. An-

other branch of the bridge connected to leads 201 and 202 comprises the resistor 207, lead 208 and resistor 209..A third branch of the bridge is constituted by resistor 211, lead 212 and resistor 213.

Lead 208 is connected by way of capacitor 214 and lead 215 to the base 216 of a transistor 217 having the emitter 218 thereof connected to ground 205. The collector 220 is connected by way of lead 226, resistor 221, lead 222 and resistor 223 to the positive terminal 224 of a suitable source of direct current potential, not shown, having the negative terminal thereof connected to ground.

The aforementioned lead 215 is connected by way of resistor 225, lead 226, capacitor 227, and lead 228 to the base 229 of a phase sensing transistor 230 having the emitter 231 thereof connected to ground 205. The lead 228 and base 229 are connected by way of resistor 232 to the positive terminal 233 or a source of direct current potential, not shown, having the other negative terminal thereof connected to ground 205. The phase sensing transistor 230 has the collector 235 thereof connected by way of lead 236, resistor 237, rectifier 238 and lead 239 to one terminal of the secondary of a transformer which may correspond to the secondary 104 of FIG. 2, the other terminal of the secondary being connected to ground 205. Lead 239 may be identical with lead 139. The primary of the transformer whose secondary supplies an alternatingcurrent to lead 239 is preferably energized from leads 201 and 202. In this way a pulsating directcurrent is applied to the collector 235, and this provides that the transistor 230 has an output only when a predetermined phase relationship exists between the voltage on the collector and the alternating current signal applied to the base thereof.

transistor 24.1 is coupled by way of lead 244, resistor.

243 and lead 236 to collector 235. The collector 252 of transistor 242 is coupled by capacitor254 and resistor 255 to the base 245 of transistor 241, and the collector 247 of transistor 241 is coupled by resistor 249 to the base 250 of transistor 242. Emitter 246 of transistor 241 is connected to ground, and transistor 242 has emitter 251 thereof connected to ground 205. As aforementioned, the collector 2520f transistor 242 is connected by way of lead 253, capacitor 254 and resistor 255 to the aforementioned lead 244. Lead 253 is connected by way of resistor 256 to the positive termi nal 257 of a suitable source of direct current potential, not shown, having the othernegative terminal thereof connected to ground 205. Lead 253 and collector 252 are also connectedby way of resistor 260 to the base 261 of an emitter follower transistor 262 having the emitter-263 thereof connected by way of relay coil 264 to ground 205. Relay 264 may control heater apparatus for varying the temperature of transducer 206. Collector 265 is connected to a suitable source of direct current energizing potential, not shown, having the other terminal thereof operatively connected to ground.

An additional transistor 270 is provided, having an emitter 271, base 272 and collector 273. The emitter and resistor 321 to the aforementioned lead 253..- The junction between resistors 321 and 280 is. connected by way of capacitor 322 to ground.

In understanding the operation of the apparatus of FIG. 4, it should be borne in mind that the circuit provides for a wide loop width and a flip-flop trip-off point adjustable over the entire range to the trip on point. The term loop width as employed herein is used to designate the magnitude range over which the variable quantity may vary between the trip on point and the trip off point. This is accomplished by utilizing the multivibrator to control its own input signal. It will be noted that while transistor 242 is conductive, which it normally is until a trip signal causes transistor 241 to conduct and transistor 242 to become nonconductive, a very small voltage drop approaching zero appears across transistor 242 and accordingly substantially zero potential is applied by way of lead 253 and resistor 380 to the collector 273 of transistor 270 to provide no energizing potential thereto. On the other hand, when the flip-flop circuit of transistors 241 and 242 renders transistor 242 non-conductive, a substantial voltage from terminal 257 appears on lead 253 providing an energizing potential to the transistor 270. Transistor 270 is referred to herein as to off transistor, whereas transistor 217 is referred to as the on transistor.

Transistor 217 amplifies the output of the bridge portion comprising resistors 203, 206, 207 and 209, and this output is amplified and applied as a signal to the base 229 of transistor 230, which is normally biased slightly beyond saturation. Transistor 230 has a pulsating direct current potential applied to the collector thereof and produces an output only when a predetermined desired phase relationship exists between the signal applied to the base 229 and the pulsed direct current signal applied to the collector 235.

Assume by way of example that with the bridge comprising resistors 203, 206, 207 and 209 balanced, so that no signal is developed at base 229, and assuming further that in this condition transistor 242 is conductive so that no substantial voltage appears on lead 253 and is applied to transistor 270, then when the trip on point is reached, that is, when the voltage difference resulting from temperature changes on transducer 206 is sufficiently great, the flip-flop circuit is caused to change to its other state, saturating transistor 241 and cutting off transistor 242. This results in the application of an energizing potential to the collector 273 of transistor 270 as well as supplying a biasing or gating resistor 211 to provide that until the desired trip of causing transistor 242 to remain cut off, causing the energizing potentialto remain on collector 273 of transistor 270, and causing the relay winding 264 to remain energized until the trip of point is reached.

It will be understood that transistor 241 may periodically return momentarily to a cut off state, but that within one cycle the multivibrator retrips, if the necessary signal is still present at base 229.

It is seen then that by the addition of another bridge resistance path in parallel with the branch of resistors 207 and 209, and the additional transistor 270, that a trip off point of adjustable sensitivity is provided to cause the relay winding 264 to be energized and thereafter deenergized at any desired value of bridge unbalance corresponding to any desired variation in the quantity which exercises control.

It should be understood that the term trip on refers to turning on transistor 164, or transistor 241, depending on the circuit employed, and may result in turning off the heat which would result in increased tempera ture at transducer 46 or 206 or increased pressure and further movement of slug 87 or 192.

As an example of the operation of the circuit of FIG. 4, assume that when relay 264 is energized it turns the heat off. Assume that the apparatus is at an initial temperature of 400, that is is desired to raise it to 500 and have the temperature stabilized between 500 and 490, a loop width" of 10. I

From previous calibrations, resistor 209 is adjusted to a value which causes that branch to balance, or produce zero output, at 500. From previous calibrations, resistor 213 isadjusted to a value which causes that branch to balance, or produce zero output, at 490. The heat is turned on. Transistor 241 is normally off and relay 264 normally deenergized. As the temperature at 206 approaches but is below 500, there is a signal on lead 208 but it is the wrong phase. After 500 has been reached and slightly passed, the signal on lead 208 becomes of the proper phase, tripping transistor 241 on, energizing transistor 270 and relay 264 and turning the heat off. With 10 unbalance inthat branch, there is now a large signal of the proper phase on lead 212, which maintans transistor 241 on or more precisely, keeps repeatedly turning it back on immediately every time it returns from its unstable or quasi-stable state to its normal stable state. As the temperature at 206 gradually falls after the heat is turned off, the signal on lead 212 diminishes in amplitude, and at balance, 490, suddenly reverses in phase, allowing transistor 241 to become of This turns the heat back on, the temperature at 206 begins to increase, and the cycle is repeated.

The circuit of FIG. 4 may be used with the differential transformer of FIG. 3 by supplying in parallel with branch 197-198 another branch including resistor 211, lead 212 and resistor 213, with appropriate connections being made.

Particular reference is made now to FIG. 9, which shows a modification of the circuits of FIGS. 2 and 5, in which one bridge has a pair of paralleled resistance paths in one branch, one path of the paralleled paths having a potentiometer therein for supplying a signal to the monostable amplifier circuit, and the other of the paralleled resistance paths having therein a potentiometer having an arm which is operatively connected to a servo motor for providing a null balance indication type of circuit. In FIG. 9, the leads 291 and 292 have an alternatingcurrent voltage impressed thereacross, and may be connected to the power supply 51 of FIG. 5, or may be connected to andsupplied from the power transformer of FIG. 2. One branch of the bridge includes a resistor 293 connected by way of lead 294 to a resistance thermometer 295, the resistance value of which varies in accordance with variations in the temperature. The lead 294 is connected to ground 205. In the other branch, one parallel resistance path includes resistor 296 connected by way of potentiometer 297 to the opposite lead 292. The arm 298 of potentiometer 297 is connected to lead 52 and supplies an input to a transistor amplifier. Lead 52 of FIG. 9 may correspond approximately to lead 113 of FIG. 2. The other paralleled resistance path includes resistor 301 and potentiometer 302 in series across leads 291 and 292. The arm 303 of potentiometer 302 is connected to lead 78', which may correspond to lead 78 of FIG. 5, it being understood that the other input terminal to-the servo amplifier, not shown, is connected to ground 205 The linkage 304 may correspond to the linkage 70 of FIG. 5.

In order that errors in the indication device connected to mechanical linkage 304 may be reduced to a minimum, it is desirable that the lead 52 be connected to a high impedance load and this is contemplated, the loadimpedance being as high as convenient in view of the transistor circuitry involved.

By adjusting the position of arm 298, the trip on? point of the amplifier circuitof FIG. 2- may be adjusted,

and this static trip may be substantially independent of tance thermometer being employed in a bridge arrangement having'three parallel circuits or three parallel resistance paths in one branch thereof. The additional path of the parallel paths of FIG. 10 includes resistor 307 and potentiometer 308 having arm 309 connected to lead 212. Accordingly, it is seen that one resistance thermometer, in this casethermometer 295, is used ina bridge arrangement which provides two signals to the monostable multivibrator and amplifier of FIG. 4 to provide both a trip. on and a trip-off signal, and'at the same time provides a signal to a servo amplifier, causing a servo motor to produce a null bal- 153, for controlling the bias on the phase sensing tran- I an integrator to prevent the circuit from tripping on at every single pulse. This effectively prevents any random noise pulses from causing a false trip, but allows a repetitive signal pulse to correctly trip the circuit.

Once the multivibrator has assumed a state in response to a signal pulse, it remains in that state until he circuit is opened at reset switch 185. I

Again by way of summarizing the operation of the circuit of FIG. 2, once the multivibrator has tripped on, a certain length of time, which is determined by the value of resistor 166 and capacitor 168, must elapse before the circuit is restored for further operation. When the flip-flop returns to its reset or original state, within one cycle, if the bridge is still above balance, it retrips. For a shut down signal, the-first time the flipflop trips is the only important occurrence. However, for turning on and off of heatersto control system pressure, the of point is also important. It should be noted that in at leastone embodiment shown the multivibrator circuit trips for a finite time, resets itself, and if told on the next cycle that it should still be tripped,

it trips again .within a cycle. Since the amount of time the flip-flop will stay tripped can be adjusted, on-off control can be stabilized byvarying the time on instead of requiring the handling of two accurate signal level points. I

In all embodiments, resistance values and potential values may be easily selected to provide for operation in the desired manner.

. In FIG. 4, the R-C circuit 32l-322-may be omitted if not needed. After transistor 241 is momentarily turned off, for one alternation transistor 242 may be on, with loss of voltage on lead 253. The R-C circuit insures that transistor 270 will not lose control during this brief period.

vThe term multivibrator amplifier as employed herein and in the claims appended hereto, includes a ance by an additional potentiometer arm. lt willbe understood that in the calibration of the circuit of FIG. 10, account is taken of the parallel resistance paths, and also in utilizing the circuitof FIG. 10, it is desirable to keep the load on leads 203 and 212 as small as possible, and to keep the terminating impedances as large as possible to reduce errors in theindication circuit to a minimum. Y I Particular reference is made again to the circuit of FIG. 2 As previously stated transistor 164 is normally cut off. It is rendered conductive by a bridge unbalance signal of the proper phase and magnitude such as signal A" of FIG. 8C. When 164 becomes conductive, the positivebias on the base of phase sensor transistor 133 is slightly decreased so thata small decrease in signal on the base 132 does not allow the multivibrator to trip off. Until the circuit is reset by a greater decrease in, signal, the multivibrator willremain on."

Particularreference is made now to FIG. 11, in which a modified circuit is shown, according to an additional embodiment of they invention. In FIG. 11 the bias con trol feedback link including rectifier 150 and resistor dual-state circuit which is in one state until a signal causes it to change to 'a second state, and which remains in the second state a substantial period of time determined at least in part by the time constant of a time delay circuit included inthe amplifier.

Whereas the invention has been shown and described with respect to some embodiments thereof which give satisfactory results, it should be understood that changes may be made and equivalents substituted with out departing from the spirit and scope of the invention.

We claim as our invention:

1. Multivibrator apparatus comprising, in combination, an input transistor adapted to have thebias on an input terminal thereof varied, the input transistor being normally'biased at a first predetermined value whereby an input signal of at least a first predetermined amplitude is required to produce. a usable output signal atan output terminal of the input transistor, a multivibrator circuit including operatively connected first and sec-. ond transistors and time constant means, the first tran- .sistor input terminal being operatively connected to said output terminal of the input transistor whereby a usable output signal from the input transistor causes the signal level at an output terminal of the multivibrator to change from a first state to a second state, the multivibrator remaining in the second state for a time period determined by the time constant of the time constant means and thereafter returning to the first state, and bias varying means including other time constant means connecting said output terminal of the multivibrator to said input terminal of the input transis' tor for altering the bias on the input transistor while the multivibrator is in the second state and remaining for at least a predetermined time interval after the multivibrator returns to the first state so that an input signal small in amplitude compared to the first predetermined input signal amplitude at the input transistor will produce a usable output signal and cause the multivibrator to switch from he first state to the second state.

2. Multivibrator apparatus for use in a control circuit of the type in which a signal of a first predetermined amplitude initiates a control operation and a signal of a second predetermined amplitude causes the control operation to continue comprising, in combination, first transistor amplifier means having the signal of the first predeterminedamplitude applied to an input terminal thereof, normally deenergized second transistor amplifier means having the signal of the second predetermined amplitude appliedto an input terminal thereof,

' first circuit means including a control transistor and having the output signal from an output terminal of the first transistor amplifier means and the output signal from an output terminal of the second transistor amplifier means coupled to a common circuit point in the first circuit means whereby both the first and second transistor amplifier means supply an input to an input terminal of the control transistor, a multivibrator having operatively connected first and second transistors, the first transistor being normally nonconductive while the multivibrator is in first state and the second transistor being normally nonconductive while the multivibrator is in a second state, second circuit means connecting an input terminal of the first transistor of the multivibrator to an output terminal at the control transistor of the first output means whereby an output signal from the control transistor causes the first transistor to become conductive and thusly causes the connected transistor to become nonconductive, and third circuit means connecting an output terminal of the second transistor to a terminal of the second transistor amplifier means whereby when the second transistor becomes nonconductive the normally deenergized second transistor amplifier means is energized in a manner to put the control transistor under the control of the signal of the second predetermined amplitude. 

1. Multivibrator apparatus comprising, in combination, an input transistor adapted to have the bias on an input terminal thereof varied, the input transistor being normally biased at a first predetermined value whereby an input signal of at least a first predetermined amplitude is required to produce a usable output signal at an output terminal of the input transistor, a multivibrator circuit including operatively connected first and second transistors and time constant means, the first transistor input terminal being operatively connected to said output terminal of the input transistor whereby a usable output signal from the input transistor causes the signal level at an output terminal of the multivibrator to change from a first state to a second state, the multivibrator remaining in the second state for a time period determined by the time constant of the time constant means and thereafter returning to the first state, and bias varying means including other time constant means connecting said output terminal of the multivibrator to said input terminal of the input transistor for altering the bias on the input transistor while the multivibrator is in the second state and remaining for at least a predetermined time interval after the multivibrator returns to the first state so that an input signal small in amplitude compared to the first predetermined input signal amplitude at the input transistor will produce a usable output signal and cause the multivibrator to switch from he first state to the second state.
 2. Multivibrator apparatus for use in a control circuit of the type in which a signal of a first predetermined amplitude initiates a control operation and a signal of a second predetermined amplitude causes the control operation to continue comprising, in combination, first transistor amplifier means having the signal of the first predetermined amplitude applied to an input terminal thereof, normally deenergized second transistor amplifier means having the signal of the second predetermined amplitude applied to an input terminal thereof, first circuit means including a control transistor and having the output signal from an output terminal of the first transistor amplifier means and the outPut signal from an output terminal of the second transistor amplifier means coupled to a common circuit point in the first circuit means whereby both the first and second transistor amplifier means supply an input to an input terminal of the control transistor, a multivibrator having operatively connected first and second transistors, the first transistor being normally nonconductive while the multivibrator is in first state and the second transistor being normally nonconductive while the multivibrator is in a second state, second circuit means connecting an input terminal of the first transistor of the multivibrator to an output terminal at the control transistor of the first output means whereby an output signal from the control transistor causes the first transistor to become conductive and thusly causes the connected transistor to become nonconductive, and third circuit means connecting an output terminal of the second transistor to a terminal of the second transistor amplifier means whereby when the second transistor becomes nonconductive the normally deenergized second transistor amplifier means is energized in a manner to put the control transistor under the control of the signal of the second predetermined amplitude. 